The present work’s originality lies in the evidence of a non negligible effect of the fluid ions’ and co-ions’ interaction with the wall surface in a microtube. This study is based on the EDL theory (Electrical Double Layer) which is developed here for a circular geometry. High electrical surface potentials are taken into account for the present study; they induce the nonlinearity of the problem’s main equation (Poisson-Boltzmann equation). The electrical field is determined, then the velocity profile and finally the Poiseuille number. We show that even with the EDL effect taken into account, the Poiseuille number does not depend on the mean velocity. Our model agrees with the experimental results for high surface potentials (> 25 mV). This is found by comparing with experiments previously carried out with microtubes ranging from 530 to 50 μm.
`Electrokinetics has become a popular method of both particulate and fluidic control in microdevices. In an effort to address the problems associated with conventional electrokinetic control, we use silver-silver chloride electrodes for low-voltage, spatially localized electrokinetic control in microfluidic devices. This work presents an analysis of the electric fields generated by silver-silver chloride electrodes and establishes a nondimensional design parameter that governs the device performance. In addition, an optimal parameter space for maximum electrode longevity is presented.
An experimental study of a submerged 125-mu m circular microscale jet impingement is presented. These jets flows are associated with low exit Reynolds number and a correspondingly high, subsonic Mach number. Detailed distributions of heated and adiabatic wall temperature, and local and average Nusselt number variations are presented for five laminar exit Reynolds numbers in the range of 690 to 1770 at three nozzle-to-surface spacings of 2, 4, and 6 times the nozzle diameter. The corresponding jet exit Mach numbers range between 0.26 and 0.63. An infrared radiometer is used in conjunction with a heated-thin-foil technique to measure detailed surface temperatures. Results indicate that the adiabatic surface temperature distribution is relatively insensitive to nozzle-to-surface spacing within the parameter range studied. With an increase in Reynolds number, the adiabatic surface temperature decreases significantly near the stagnation point. The average Nusselt numbers are higher compared to Martin's correlation [1] for large Reynolds numbers. A similar observation has been reported previously in a numerical study on microscale jet impingement [5] and attributed to compressibility of the flow and the possible existence of a slip flow.
Abstract By solving Maxwell's equations, we observed photon localization and strong electromagnetic field enhancement in laser-irradiated, one-dimensional random multilayer and two-dimensional random media, with particle size around the laser wavelength. Higher refractive index contrast and degree of randomness result in stronger localization. The probability density and the location of enhanced fields are investigated as functions of refractive index and particle size distribution. For weakly dissipative media, local absorption enhancement is observed, and the expectation intensity distribution is obtained by averaging among many realizations. For comparison, the equation of radiative transfer (ERT) is also solved for random porous media, using the two-flux model. Since no interference effects are allowed, the classical diffusion, rather than localization, is predicted. Consequently, ERT can represent a good statistical average of the intensities only as absorption is dominant over localization. As expected, the particle treatment of ERT does not allow for predicting photon localization and field enhancement. 236pt
The thickness of the interfacial region dividing bulk liquid and vapor regions is typically on the order of a few molecular diameters. Furthermore, in systems where the characteristic length scale is the same order of magnitude as the thickness of the interface such as a thin liquid film on a solid surface, behavior may be different than that for larger systems. The small thickness of such films leads to difficult experimental observation of phenomena within various regions of the film: the wall-affected region, the bulk liquid, and the liquid-vapor interfacial region. A hybrid simulation methodology is applied that combines a deterministic molecular dynamics simulation of the liquid regions with a stochastic treatment of the far-field vapor region boundary. In this simulation scheme, the imposed far-field pressure may be held fired or iterated as the simulation is advanced in time until the mass in the system stabilizes at the specified temperature, which establishes the equilibrium saturation vapor pressure for the specified temperature as dictated by the intermolecular force interaction models for the fluid and molecules near the solid surface. Simulation results are presented for an argon liquid film on a solid metallic surface.
